JPH11264778A - Optical fiber type pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber intra-cylinder pressure sensor which does not require a complicated processing of constituent members of engine, is equipped with a high sensitivity of sensor, and excels in the long-term stability. SOLUTION: This optical fiber type pressure sensor includes at least one optical fiber and a means to convert the pressures at points in N pieces into displacements, and an initial flexural deflection is given to the optical fiber previously by a means to give deflection to the optical fiber which is added to the above-mentioned converting means, and bending stress is given to the optical fiber in accordance with the change of the pressure by the converting means, and the pressure is determined from the change in the photo-quantity passing through the optical fiber. Within the measurable range of passing photo- quantity, the initial flexural deflection amount to be previously given to the optical fiber is set so that the product of A and B maximizes, where A is (N-1)th power of the passing photo-quantity in the optical fiber having initial flexural deflection in one place while B is the change of the photo-quantity in the fiber when the flexural deflection complying with the pressure change is superposed on the initial flexural deflection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the measurement of pressure in a cylinder (in-cylinder pressure) and the measurement of other pressures performed for engine control.

[0002]

2. Description of the Related Art As a conventional technique relating to pressure measurement, a case of measuring in-cylinder pressure (including knock pressure) for controlling an automobile engine will be described below. As a technique for detecting an in-cylinder pressure and vibration (knock) of an engine and reflecting the result in engine control, there is a technique utilizing a piezo effect, and there is a pressure sensor described in JP-A-3-237761. On the other hand, an optical in-cylinder pressure sensor using an optical fiber has been proposed in order to perform sensing suitable for an environment with much electrical noise such as an engine room. These are not only resistant to electric disturbance but also can measure the in-cylinder pressure with higher accuracy than those using the piezo effect. One example is disclosed in JP-A-7-306109.
In the publication, a birefringent optical fiber is adopted, a gasket is processed, pressure transmitting means are provided for each of a plurality of cylinders of the engine, and the optical fiber is built in the gasket, thereby reducing pressure and vibration in the cylinder. There has been proposed a technique for capturing time change in detail for each cylinder.

[0003]

The above-mentioned prior art in-cylinder pressure sensor is suitable for measuring an in-cylinder pressure of about 10 MPa. However, a knock signal having a pressure of about 1/1000 of the in-cylinder pressure is detected. There is a problem that it is difficult, and it is required to detect a knock signal stably over a long period of time.

Further, since the in-cylinder pressure sensor is used for controlling the engine, it is necessary to detect a stable signal for a long period of time. For that purpose, it is required to suppress deterioration such as breakage of the optical fiber due to strain applied by the means for bending the optical fiber added to the means for converting pressure into displacement, and peeling of the optical fiber coating due to lateral pressure. ing.

[0005] Furthermore, in order to manufacture at low cost, it is required to realize the above-mentioned problem with a simple structure.

An object of the present invention is to provide an optical fiber in-cylinder pressure sensor having high sensitivity and excellent long-term stability without requiring complicated processing of engine components.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has at least one optical fiber and means for converting pressure into displacement at each of N pressures. A means for imparting a bending deflection to the optical fiber added to the means for converting the pressure into a displacement gives an initial bending deflection to the optical fiber in advance, and further gives a bending deflection to the optical fiber in response to the change in the pressure, so that the inside of the optical fiber is bent. In an optical fiber type pressure sensor that detects the pressure from the change in the amount of light passing through, within the measurable range of the amount of light passing, the amount of (N
-1) The initial bending amount to be applied to the optical fiber is set in advance so that the product of the power and (the amount of change in the amount of transmitted light due to bending of the optical fiber according to the pressure change) is maximized. .

[0008] A second means of the present invention for solving the above-mentioned problems comprises an optical fiber, and initial deflection applying means arranged at N positions in the longitudinal direction of the optical fiber and applying initial deflection to the optical fiber at each of the positions. Pressure conversion means for superimposing a deflection amount according to a change in pressure to be measured, which is added to each of the initial deflection applying means, on the initial deflection of the optical fiber, and an amount of light passing through the optical fiber. In the optical fiber pressure sensor which detects the change in pressure from the change in the pressure, within the measurable range of the amount of transmitted light, the (N-1) th power of (the amount of transmitted light of the optical fiber having one initial bending deflection) and The initial bending given to the optical fiber in advance so that the product of (the amount of change in the amount of light passing through the optical fiber in which the bending according to the pressure change is superimposed on the initial bending) is maximized. Wherein the Wami amount is set.

The optical fiber type pressure sensor according to the first and second means may measure the pressure of a multi-cylinder engine.

In the above-mentioned optical fiber type pressure sensor for measuring the pressure of the multi-cylinder engine, the pressure of (the amount of change in the amount of light passing through the optical fiber in which the bending according to the pressure change is superimposed on the initial bending). The change may be a change in cylinder pressure due to engine knock.

In the optical fiber type pressure sensor described in each of the above items, the amount of light passed by one initial bending is set to be at least 0.8 when the amount of input light is 1.
It is desirable that the amount of initial bending given to the optical fiber be set in advance.

The optical fiber type pressure sensor described in each of the above items may be built in a gasket used by being inserted between the cylinder and the cylinder head.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described.
This will be described in detail with reference to the drawings. FIG. 2 illustrates the mounting state of the optical fiber type pressure sensor according to the present invention in a case where the optical fiber pressure sensor is mounted on an engine gasket 40 as an example, with a focus on a combustion pressure sensing portion. FIG. 2 (a)
A part of the section taken along line AA of FIG. The illustrated optical fiber type pressure sensor has a disc-shaped sensor block 20.
And an optical fiber 50 disposed so as to pass through the inside of the sensor block 20. The sensor block 20 and the optical fiber 50 are housed in an optical fiber passage formed inside the gasket 40. ing.

The gasket 40 is formed of three layers in the thickness direction, namely, an upper plate 40a, a middle plate 40b, and a lower plate 40c.
They are joined together to form one gasket 40. The side of each cylinder of the middle plate 40b is cut out in a circular shape, and vacancies corresponding to the number of cylinders are provided in a line, and the disc-shaped sensor block 20 is fitted into each of the vacancies. ing. An optical fiber passage 10a is formed in a groove shape on the upper surface of the middle plate 40b (surface on the upper plate 40a side) so as to form a straight line connecting the circular space and both ends in the longitudinal direction of the gasket 40. The sensor block 20 is formed by joining an upper upper sensor block 20a and a lower lower sensor block 20b to each other, and an upper surface of the lower sensor block 20b is fitted into the circular space of the middle plate 40b. In this state, the intermediate plate 40b is flush with the bottom surface of the optical fiber passage 10a. The upper sensor block 20a has an annular shape,
A groove-shaped optical fiber passage 10b is formed at a position on the lower surface where the straight line passes. In the center of the upper surface of the lower sensor block 20b, a projecting portion (initial deflection applying means) 23 having a rectangular cross section and extending in a direction orthogonal to the straight line is provided.
Are formed, and the lower surface (the lower plate 40) of the lower sensor block 20b is formed.
c), a disc-shaped recess 11 is formed concentrically with the circular space. That is, the thickness of the lower sensor block 20b is reduced by forming the disc-shaped recess 11, and as a result, a circular diaphragm 21 is formed in the lower sensor block 20b. The disk-shaped recess 11 is formed in the gasket 40 by an internal pressure introduction path formed in a groove shape on the lower surface of the middle plate 40b in a direction perpendicular to the straight line.
Of the cylinder bore. The inner diameter of the annular upper sensor block 20a is equal to the lower sensor block 20a.
b The size is substantially the same as the inner diameter of the disc-shaped recess 11 on the lower surface.

The optical fiber passages 10a and 10b are straight, and the optical fiber 50 is connected to the optical fiber passages 10a and 10a.
10b, it is arranged so as to extend over the protrusion 23. One end of the optical fiber 50 is connected to the light source 60,
The other end is connected to a light receiver 61 having a photoelectric module. The electric signal output from the light receiver 61 is input to a controller (not shown), converted into a pressure value, and displayed and output. That is, the in-cylinder pressure measuring device is configured to include the light source 60, the gasket 40 containing the optical fiber pressure sensor, the light receiver 61, and the controller.

Here, as a means for converting pressure into displacement, a diaphragm will be described as an example. In this manner, by tightening the gasket 40 to the engine body 25, the upper portion of the diaphragm 21 or the diaphragm portion of the sensor block 20b communicates with the outside of the cylinder, and the lower portion communicates with the inside of the cylinder. Is formed. Due to this pressure difference, the diaphragm 21 is deformed upwardly convex, and this deformation pushes the projection 23 disposed on the upper surface of the diaphragm 21 further upward, and is guided on the projection 23 to reduce the initial deflection. Optical fiber 50 added
The bending deflection is further added to the above. That is, the diaphragm 21 and the upper sensor block 20a constitute a pressure conversion unit that converts a change in the in-cylinder pressure into a change in the amount of deflection of the optical fiber 50.

The optical fiber 50 is provided with an optical fiber passage 10b cut on the upper sensor block 20a side (the optical fiber passage 10b may be formed on the lower sensor block 20b side, in which case, the bottom surface of the optical fiber passage 10b Sensor block 20 so that
b, a circular recess is formed on the upper surface of the sensor block 20 through the optical fiber passage 10b on the opposite side, passing over the projection 23 provided on the diaphragm 21 on the diaphragm 21. The gasket 40 is installed along the optical fiber passage 10a. In addition, the width of the projection 23 together with the width of the optical fiber passages 10a and 10b (in the direction perpendicular to the straight line) so that the optical fiber 50 does not come off the projection 23 even when the optical fiber 50 is shifted laterally in the Length). at least,
The width is larger than the width of the optical fiber passage 10b.

In this manner, the optical fiber 50 is divided into two locations on the inner peripheral side of the upper sensor block 20a of the optical fiber passage 10b and two locations on the tip of the projection 23 of the diaphragm 21 (on the top view of the projection 23). The optical fiber 50 is preliminarily bent in advance by supporting the optical fiber 50 at two points on the bottom surface of the optical fiber passage 10b of the sensor block 20.

FIG. 3 schematically shows a measurement example of the ratio of the amount of transmitted light / the amount of incident light of the optical fiber to the amount of bending of the optical fiber (hereinafter referred to as the amount of transmitted light). The amount of light passing through the optical fiber rapidly decreases from an appropriate bending deflection position depending on the optical characteristics of the optical fiber and the supporting structure of the optical fiber. When the cylinder internal pressure increases with combustion, a pressure 70 is applied from below the diaphragm 21 in the embodiment shown in FIG. Accordingly, the amount of bending of the optical fiber is reduced to the initial set value H0 (the height of the projection 23 of the diaphragm 21).
In addition, as shown in FIG. 3, the amount of light passing through the optical fiber 50 increases from the initial set value α (H0) by αH.
(H0 + ΔH). Therefore, if the relationship between the pressure due to combustion and the amount of passing light is determined in advance, the in-cylinder pressure can be known by measuring the amount of passing light.

Conventionally, the height of the diaphragm projection is set in the quasi-linear region (the amount of transmitted light per spot is set to 0.8 or less) in the curve of the amount of transmitted light versus the amount of deflection of the optical fiber shown in FIG. As described above, the sensor is designed so that the knock pressure can be detected with high sensitivity, assuming the case of one cylinder. The amount of light passing through the optical fiber α (H0) with respect to the projection height H0 of the diaphragm is the displacement Δ of the diaphragm corresponding to the knock pressure.
H changes by Δα.

Δα = α (H0 + ΔH) −α (H0) (1) With respect to the input light amount Iin, the output light amount at the time of initial setting (the bending amount of the optical fiber is the protrusion height H0) is Iout, and the knock pressure is When it occurs (the amount of bending of the optical fiber is equal to the protrusion height H0 + Δ
Assuming that the output light amount of H) is Iout ', in the case of one cylinder, that is, in the case of one measurement point, the change in the passing light amount with respect to the knock pressure ΔIout (knock output) is given by the following equation.

Iout = α (H0) × Iin (2) Iout ′ = α (H0 + ΔH) × Iin (3) ΔIout = Iout′−Iout = Δα × Iin (4) In this case, the knock output does not depend on the set light output α (H0) shown in FIG. 3 but depends only on the variation Δα. Therefore, the output of the sensor is constant in the quasi-linear region.
And it turns out that the sensitivity is the highest.

However, when there are a plurality of measurement points, for example, when the in-cylinder pressure of four cylinders is detected by one optical fiber, a change in the passing light amount with respect to knock ΔIout (knock output) is given by the following equation.

Iout = (α (H0)) ⁴ × Iin (5) Iout ′ = α (H0 + ΔH) × (α (H0)) ³ × Iin (6) ΔIout = Iout′−Iout = Δα × ( α (H0)) ³ × Iin (7) Therefore, in the case of N cylinders, the knock output is the set light output α.
It is proportional to the product of (H0) raised to the (N−1) th power and the change amount Δα.
That is, as shown in FIG. 1, within the measurable range of the passing light amount, the (N-1) th power of (the passing light amount of the optical fiber having one initial bending deflection) and (the initial bending deflection and the pressure due to knocking) By setting the amount of initial bending deflection given to the optical fiber in advance so that the product of the amount of light passing through the optical fiber when the bending deflection according to the change is superimposed is maximized, the most sensitive sensor You can get the output. Since the optical fiber for the sensor has a high sensitivity to bending (change in the amount of transmitted light), a small amount of ΔH
(For example, 10 μm), sufficient sensitivity can be obtained. When ΔH is very small, the linearity of the sensor output is sufficiently maintained even in a region other than the quasi-linear region of FIG.

Further, since this optical fiber type pressure sensor is used for engine control, stable signal detection is required for a long period of time. For this purpose, damages due to distortion of the optical fiber, which greatly affects the characteristics of the sensor, and means for bending the optical fiber provided in the sensor block 20 (diaphragm 21, projection 23, upper sensor block 2,
It is required to suppress deterioration such as peeling of the optical fiber coating due to the lateral pressure added by Oa).

In FIG. 3, the initial value of the height of the diaphragm protrusion in this embodiment corresponds to a region where the amount of bending deflection is lower than the quasi-linear region of the curve of the amount of transmitted light versus the amount of bending of the optical fiber. Therefore, in the embodiment of the present invention, compared with the case where the optical fiber is set in the quasi-linear region,
The strain and the side pressure applied to the optical fiber are reduced, the breakage of the optical fiber and the peeling of the optical fiber coating are suppressed, and the service life of the sensor can be extended.

FIG. 4 shows a step index type single mode optical fiber (core diameter 5.14 μm, clad diameter 125 μm, relative refractive index 0.1) as an in-cylinder pressure sensor for automobiles.
63%, cutoff wavelength 0.56 μm), the pressure of the four cylinders is detected, and the base interval S of the sensor block (the inner diameter of the upper sensor block 20a) is 4 mm as the optical fiber supporting dimension. Optical fiber passage height 0.18 mm, protrusion length (length between optical fiber contact points)
The relationship between the amount of light passing through the sensor and the amount of initial bending of the optical fiber (the height of the projection 23) is shown by taking the case of 0.8 mm as an example. FIG. 5 shows the knock output (when the input light amount is 40 μW, and the diaphragm displacement ΔH is 0.1 μm due to the knock).
And initial bending deflection of optical fiber (height of protrusion 23)
Shows the relationship. FIG. 6 shows the relationship between the maximum strain applied to the optical fiber (the maximum value of the strain% at the six contact points) and the initial bending deflection of the optical fiber (the height of the protrusion 23). FIG. 7 shows the relationship between the maximum lateral pressure applied to the optical fiber (the maximum value of the forces applied to the optical fiber at the six locations) and the amount of initial bending of the optical fiber (the height of the projection 23).

4 and 5, the amount of initial bending deflection given to the optical fiber in advance, that is, the knock output is the largest when the projection height is 0.12 mm, and the amount of light transmitted by one initial bending deflection is 0.87. Was. In this case, the protrusion height is set in a region where the amount of deflection is lower than the quasi-linear region of the curve of the amount of transmitted light versus the amount of deflection of the optical fiber.
Therefore, from FIGS. 4 and 5, the strain and the side pressure applied to the optical fiber are reduced, and the breakage of the optical fiber and the peeling of the optical fiber coating are suppressed as compared with the case where the projection height is set in the conventional quasi-linear region. Therefore, the life of the sensor can be extended.

When a step index type single mode optical fiber is used for a sensor and the in-cylinder pressure of N cylinders is measured, the amount of light passing through one initial bending deflection is at least 0.8 with respect to the amount of input light. Within the range of the initial bending deflection given to the optical fiber in advance, (1
The product of (N-1) raised to the power of (N-1) raised to the power of (the amount of light passing through the optical fiber due to the initial bending deflection of the portion) and (the amount of change in the amount of light passing through the optical fiber when bending deflection according to the pressure change due to knocking is superimposed on the initial deflection) There is a setting value that maximizes. By using the set value of the initial bending deflection amount, the sensitivity of the in-cylinder pressure and the vibration (knock) signal can be detected to the maximum. Further, the strain and the side pressure applied to the optical fiber are reduced, and the breakage of the optical fiber and the peeling of the optical fiber coating are suppressed, so that the service life of the sensor can be extended.

[0030]

According to the present invention, within the measurable range of the passing light amount, (the passing light amount of the optical fiber having one initial bending deflection) raised to the (N-1) th power and (the knock in addition to the initial bending) The in-cylinder pressure and vibration are set in advance by setting the amount of initial bending deflection given to the optical fiber so as to maximize the product of the amount of light passing through the optical fiber when the bending deflection according to the pressure change is superimposed. (Knock) Signal sensitivity can be maximized. Further, the strain and the side pressure applied to the optical fiber are reduced, and the breakage of the optical fiber and the peeling of the optical fiber coating are suppressed, so that the service life of the sensor can be extended.

[Brief description of the drawings]

FIG. 1 is a graph illustrating a set value of an initial bending deflection of an optical fiber in-cylinder pressure sensor according to a first embodiment of the present invention.

FIGS. 2A and 2B are a perspective view and a partial cross-sectional view illustrating a mounted state of the optical fiber in-cylinder pressure sensor according to the first embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the amount of bending of an optical fiber and the amount of light passing through the optical fiber.

FIG. 4 is a graph showing an example of the relationship between the amount of bending light of an optical fiber and the amount of light passing through the optical fiber.

FIG. 5 is a graph illustrating an example of a relationship between an initial bending amount of an optical fiber and a knock output.

FIG. 6 is a graph showing an example of the relationship between the amount of bending of an optical fiber and the maximum strain applied to the optical fiber.

FIG. 7 is a graph showing an example of the relationship between the amount of bending of an optical fiber and the maximum lateral pressure applied to the optical fiber.

[Explanation of symbols]

 10a Optical fiber passage in gasket 10b Optical fiber passage in sensor block 11 Depression 20 Sensor block 20a Upper sensor block 20b Lower sensor block 21 Diaphragm 23 Diaphragm projection 25 Engine body 40 Gasket 40a Upper plate of gasket 40b Middle plate of gasket 40c lower plate of gasket 50 optical fiber 60 light source 61 light receiver 62 radiation light 70 cylinder pressure

Claims (6)

[Claims] 1. At least one optical fiber and means for converting pressure into displacement for each of N pressures,
A means for imparting a bending deflection to the optical fiber added to the means for converting the pressure into a displacement gives an initial bending deflection to the optical fiber in advance, and further gives a bending deflection to the optical fiber in accordance with the change in the pressure, thereby providing a bending inside the optical fiber. In an optical fiber pressure sensor that detects the pressure from a change in the amount of light passing through the optical fiber pressure sensor, the (N-1) th power of (the amount of light passed by one initial bending deflection) and (the aforementioned An optical fiber type pressure sensor characterized in that an initial bending amount to be applied to an optical fiber is set in advance so that a product of a bending light amount of the optical fiber according to a pressure change and an amount of light passing therethrough is maximized. 2. An optical fiber, an initial flexure applying means arranged at N locations in the longitudinal direction of the optical fiber and imparting initial flexure to the optical fiber at each location, and each of the initial flexure imparting means is measured by being added to the initial flexure imparting means. Pressure conversion means for superimposing the amount of deflection according to the change in pressure on the initial deflection of the optical fiber, and detecting the change in pressure from the change in the amount of light passing through the optical fiber. In the fiber pressure sensor, within the measurable range of the passing light amount, (the passing light amount of the optical fiber having one initial bending deflection) raised to the (N−1) th power and (the initial bending deflection according to the pressure change) The amount of initial bending deflection given to the optical fiber is set in advance so that the product of the amount of light passing through the optical fiber on which the bending deflection is superimposed is maximized. Optical fiber pressure sensor. 3. An optical fiber pressure sensor according to claim 1, wherein the pressure of the multi-cylinder of the engine is measured. 4. The optical fiber pressure sensor according to claim 3, wherein the change in the pressure of (the amount of change in the amount of light passing through the optical fiber in which the bending according to the pressure change is superimposed on the initial bending) is an engine. An optical fiber type pressure sensor characterized by a change in in-cylinder pressure due to knocking. 5. The optical fiber pressure sensor according to claim 1, wherein the amount of light transmitted through one initial bending deflection is at least 0.8 when the amount of input light is 1. An optical fiber type pressure sensor wherein an initial bending amount to be given to an optical fiber is set in advance. 6. A gasket which is used by being inserted between a cylinder and a cylinder head, wherein the gasket incorporates the optical fiber pressure sensor according to any one of claims 1 to 5. gasket.